Working in that industry for more than three decades, I
really admire Mr. Erlachers attitude.
My first thing with 8051 was designing a resident monitor-
replacing the need for ICE´s etc.
And well seasonded hands out there in the vineyards of
electronics know why.

A resident debugger ist most useful in combination with a ROM- simulator.

Here are some of the tools:

http://www.ustr.net/files/download.shtml
http://www.raisonance.com/products/8051/MON51.php
http://www.noicedebugger.com/
http://www.allen-systems.com/md51.htm
http://web.kd0yu.com/files.php
http://www.dtweed.com/circuitce...acro1.html

By the way, Keil´s monitor is resident: A small resident portion
interacts with a more sophisticated win based frame. Quite
nice, if ROM is limited and one got a modern laptop.

By the way: AD ADuC8xx are equipped with a resident debugger,
communicating with the outside world via a one wire interface.
You see, even most modern manufacturers accept the need for
resident debuggers ;o))

So old hands, keep on doing while the youngsters are discussing..

Regards

wolf